The present invention relates to a seal assembly of the so-called box type, designed to be inserted between two members in relative rotation, in particular between an axle, for example the axle of an industrial vehicle, and a seat through which the axle passes, in order to close with a fluid-tight seal the seat within which are normally housed the rolling bearings which support the axle (if this is of the rotating type), or else which support the wheel hubs rotating on the axle, the said axle, in this latter case, being anchored fixed to the chassis of the vehicle. Also housed inside the seat is the grease necessary for lubrication of the bearings.
Known seal assemblies of the type referred to above include a bushing that can be fitted to the axle in such a way that it is fixed thereto and is fluid-tight, and a gasket that includes a metal reinforcement which can be fitted in a fluid-tight way in the seat, and a seal member made of elastomeric material (rubber) and provided with a plurality of annular lips, the main one of which is loaded by a garter spring and co-operates radially in a sliding way with a sleeve-type coupling portion of the bushing on the axle. The bushing is further provided, on the end opposite to the direction of its introduction into the seat, with a flange portion which carries additional sealing lips, called dust lips in that they face towards the outside of the seat. In this way, the dust lips and the flange portion of the bushing prevent external contaminants (water, dust, mud, etc.) from penetrating inside the seal assembly and thus damaging the main lip. Since the latter lip remains facing the lubricating grease, it prevents the said grease from coming out and is at the same time lubricated thereby in order to reduce sliding friction on the sleeve portion of the bushing on which it exerts a dynamic sealing action
Seal assemblies of the type referred to above are quite satisfactory but present a number of drawbacks. In particular, the part of the reinforcement that faces towards the outside of the seat, and is thus in direct contact with external contaminants, is easily oxidized, so that the dust lips get damaged. The dust lips lose their sealing action, so leading to the main lip getting damaged and to the seal gasket becoming unserviceable. On the other hand, fabrication of the entire reinforcement using oxidation-resistant materials would from one standpoint be too costly and from the other standpoint could create problems of adhesion to the elastomeric sealing member, which is usually fixed so that it is integral with the reinforcement by a process of vulcanization-phase bonding. Also the making of the reinforcement with a number of elements made of different materials is problematical in that the problem of obtaining reciprocal fixing of these elements in an economic way and without any damage would have to be solved. Finally, the sealing action of the dust lips is not always very efficient, and in the long run this brings about damaging of the gasket in any case.
The object of the present invention is thus that of improving the known box-type seal assemblies, ensuring a longer duration of the gasket, at the same time cutting down on overall dimensions and on costs.
According to the present invention, it is provided a seal assembly able to be inserted between two members in relative rotation, in which a bushing able to be fitted in a fixed and fluid-tight way to a first one of said members co-operates in a fluid-tight way with a gasket which comprises a substantially rigid reinforcement able to be coupled in a fluid-tight way to a second of said members, and a first sealing member carried by the reinforcement so that it is integral with the latter, the said first sealing member being made of elastomeric material and being provided with a first annular lip co-operating radially in a sliding way with a sleeve-type coupling portion of the bushing, which is mounted coaxially with the first lip and with a corresponding sleeve-type coupling portion of the reinforcement; characterized in that one face of the sleeve portion of the reinforcement facing the bushing is provided, on the side opposite to the said first lip, with a seat in which a substantially rigid ring is mounted in a blocked way, the ring being made of an oxidation-resistant material and extending substantially in front of a flange portion of the bushing, which in turn carries, integral with it, a second sealing member made of elastomeric material, the said second sealing member being provided with at least one annular lip co-operating in a sliding and fluid-tight way with a sealing surface of the said ring.
As compared to the known solutions, the seal assembly according to the present invention presents numerous advantages. In the first place, the annular lip carried by the flange portion of the bushing (i.e., the lip most exposed to the action of the external agents) does not co-operate in a sliding way directly with the reinforcement of the gasket, but with the ring made of oxidation-resistant material, which, albeit coming into direct contact with the external contaminants, is not oxidized, and consequently does not damage the lip that slides on it. As a result, the latter lip remains efficient for a long time, so preserving the sealing member of the gasket, which in turn will have a longer service life. In addition, the ring made of oxidation-resistant material constitutes only one small part of the reinforcement of the gasket, which is instead made, as a whole, of traditional materials, and hence at a contained cost, and without creating any problem of adhesion of the corresponding sealing member made of elastomeric material. On the other hand, also the assembly of the ring on the reinforcement is, according to the invention and as will be clarified in what follows, extremely simple and economical, and is achieved without any risk of damage to the various components of the seal assembly.
In addition, the seal assembly according to the invention ensures a far more efficient sealing action than do known solutions, owing to the presence of a number of annular lips operating in different directions, the said seal assembly presenting at the same time extremely contained overall dimensions. The seal assembly according to the invention may, in fact, comprise, as will emerge from the ensuing description, sealing lips acting both in an axial direction and in a radial direction in opposite senses.